The correct intracellular targeting of protein kinases and phosphatases confers specificity to the enzymes, in part, by placing them in close proximity to their preferred substrates. A prototypic example that incorporates localization is the A-Kinase Anchor Proteins (AKAPs). This family of proteins maintains the cyclic AMP dependent protein kinase (PKA) in specific subcellular compartments, thereby ensuring accessibility of the kinase to a limited number of substrates in a particular location. This compartmentalization occurs through the interaction of the docking domains of the regulatory subunit of PKA with a conserved "anchoring site" on the various AKAPs. AKAPs are also scaffold proteins involved in localizing phosphatases as well as protein kinase C (PKC) at a single site, thus affording a possible mechanism for integrating multiple signal transduction pathways. Since the mechanism for targeting PKC is variable, we are focussing on a necessary important event in the maturation process of the enzyme. A pressing issue then is to define the molecular basis for discriminating these targeting interactions. Thus, the long-term objective of our work is to determine how specific protein:protein interactions control the localization of protein kinases in the cell. The goals of this proposal are directed towards understanding the interactions responsible for the localization of the protein kinases PKA and PKC. Our specific aims are directed towards: I. Elucidating the specificity of the interactions of AKAPs with the type I and type II PKA. II. Defining the molecular determinants for anchoring at the Centrosome. III. Elucidating the structural determinants for interaction of PKC with PDK-1 and HSP70.